Method for the manufacture of tin plate



y 1967 R.J. BENTZ ETAL 3,331,230

METHOD FOR THE MANUFACTURE OF TIN PLATE Filed Oct. 13, 1964 DRIER m a 2a 4 g I I J m PICKLING M AND RINSE ouavcw -7 RINSE PLAT/N6 E I58 I7INVENTORS. RONALD J. BENTZ and ANER N. LAUBSCHER PERCENT REDUCTIONAttorney United States Patent 3,331,230 METHOD FOR THE MANUFACTURE OFTIN PLATE Ronald J. Bentz, Forest Hills Borough, and Aner N.

Laubscher, Penn Hills, Township, Allegheny County,

Pa., assignors to United States Steel Corporation, a

corporation of Delaware Filed Oct. 13, 1964, Ser. No. 403,612 7 Claims.(CI. 72-42) This invention relates to the manufacture of tin plate andin particular to that method of manufacture which is characterized bycold reduction of a tinned steel strip to finish-gage and coatingweight.

It has been established that tin plate of exceptional thinness andstrength can be produced by rolling low carbon steel strip to anintermediate gage greater than the desired finish-gage, coating thestrip with tin and then cold reducing the resulting tinned strip tofinish-gage and finish-coating weight. The resulting product has beentermed reduced last-tin plate. The final cold reduction step requiresthe use of a rolling coolant'lubricant which must be removed in orderthat the tinned surface may be chemically treated to resist staining.And to facilitate handling in subsequent fabricating operations, thechemically treated surface must then be reoiled with a lubricantcompatible with the lacquers and enamels used therein. The amount ofthis lubricant is critical; a film of more than about 2 guns. per basebox causes difficulties in soldering and lacquering. Since a base box oftin plate consists of 31,360 sq. in. (217.77 sq. ft.) of plate area,oiling involves spreading extremely minute (less than 2 gms.) quantityof lubricant uniformly over about 435% sq. ft. of surface. While such isaccomplished by the foregoing sequence of operations, the costs ofcleaning and handling the cold reduced tinned strip through separatechemical treating and oiling facilities are considerable. It has beenproposed to avoid these costs by substituting for the conventionalcoolant-lubricant used in the final cold reduction step an emulsion ofthe final oiling agent in an aqueous solution of the chemical treatingagent. However, the necessary precise control of the oil deposition hasnever been achieved in such practice.

It is an object of the present invention to provide a method whereby theaforementioned difficulties in the production of reduced last-tin platemay be overcome, and the costs of production greatly reduced.

The accomplishment of this and other objects will be set forth in thefollowing specification to be read in conjunction with the attacheddrawings wherein:

FIGURE 1 is a diagrammatic showing of the processing steps of thepresent invention up to the final cold reduction step.

FIGURE 2 is a diagrammatic showing of a cold reduction mill and certainauxiliary equipment essential to completion of processing in accordancewith practices of the present invention, and

FIGURE 3 is a graph showing the relative rolling force required ineffecting various amounts of cold reduction in a tin coated steel strip.Curve A of this figure obtains when the tinned strip is rolled using theconventional practice of flooding the strip and rolls with acoolantlubricant solution; curves B, C, D, E and F, when the onlylubrication provided is a film of 0.20, 0.58, 0.69. 1.0 and 1.2 gmslbb.of cottonseed oil respectively applied to the strip prior to rolling.

We have discovered:

(i) that the presence of an oil film, particularly a film of cottonseedoil or palm oil, of as little as 1 gm. per base box on the surface of atinned low carbon steel strip provides sufficient lubrication to permitcold re- 3,331,230 Patented July 18, 1967 "ice duction of as much as toto be made in such strip,

(2) hat such a film of oil is reduced in substantially direct proportionto the amount of the cold reduction effected on the strip, and that thisresult obtains with films up to at least 5 gms./bb. even when the stripand the rolls of the mill are flooded with copious quantities of coolingwater, and

(3) that the presence of such films up to at least 5 gms./bb. on thesurface of tinned strip does not interfere in the treatment of suchsurface with the aqueous solutions of chromic acid and/or chromate saltscommonly used to impart stain resistance.

These discoveries permit rearrangement of the operational steps in theproduction of reduced lasttin plate and the elimination of certaintroublesome practices heretofore believed necessary.

Referring now to FIGURE 1, the method of the present invention comprisespassing a strand of low carbon steel strip of any analysis suitable tothe production of tin plate, which has been previously rolled to anintermediate gage, cleaned and annealed, from an uncoiler 1 throughconventional pickling and tin plating units 2 and 3 respectively. Thetin coated strip is then passed through rinsing and drying units 4 and 5into a suitable furnace 6 wherein the tin coating is melted andbrightened. The strip leaves the furnace through a quench tank 7 andpasses to a drier 8. Units 6 and 7 are bypassed if matte-finished tinplate is desired. At this point processing departs from conventionalreduced last" practices and the tinned strip is passed through an oiler9 where a film of either cottonseed or palm oil is applied to itssurfaces before rewinding on recoiler 10. Oilcr 9 may be either anelectrostatic or an emulsion type of oiler, however, for presentpurposes it must be operated to apply an oil film of between 1 and 5gms./bb. If an emulsion oiler is used, a hot air drier, not shown,should be interposed between the oiler and recoiler 10.

As evident from the curves of FIGURE 3, at least 1.0 gm. per base box ofoil must be applied to afiord tolerable lubrication during rolling,while a film of about 1.2 gmJbb. provides lubricity fully equivalent ofthat achieved in conventional rolling ractices. As previously mentioned.the cold reduction reduces this oil film in substantially the sameproportion as the strip and the coating. Accordingly, the thickness ofoil on the finished product can be controlled by regulating the amountof the oil-precoat in relation to the percent reduction to be effectedin the next step of the process. For some products a final oil film ofless than 0.5 gm./bb. is sufiicient; for others, a film of as much as 1gm./bb. may be used. It is important, however. that the final film doesnot exceed about 2 gms./bb. if difficulties in soldering and lacqueringof the product are to be avoided; thus within the range 1 to 5 gms./bb.of oil which can be applied in the pre-oiling step, the maximum willdecrease as the amount of reduction to be taken in the subsequent coldreduction step is decreased.

To complete the processing in accordance with present invention, thetinned and pre-oiled strip from recoiler 10 is passed through the coldreduction mill 11 of FIGURE 2. A suitable mill is comprised of twofour-high stands 12A and 12B arranged in tandem, an uncoiler 13, arecoiler 20 and the usual fore and aft tensioning devices 14A and Brespectively which also serve to maintain a substantially horizontalpassline through the mill. Approximately 99% of the reduction necessaryto bring the strip to finish gage and coating weight is taken on thefirst stand 12A; the stand 12B serving mainly as a flattening pass.Reduction can be accomplished in a single pass through a single standmill; however, two-stage reduction of the above character is preferablesince it permits correction of strip shape and surface appearance.

For the purposes of the present invention, a pair of spray pipes A and15B are provided between stands 12A and B. These pipes are disposed todirect streams of treating solution against the surfaces of the strip asit emerges from the stand 12A. The solution may be any of the aqueouschromium containing solutions commonly used to imp-art stain-resistanceto tin plate; a 1 to 2% (by weight) solution of chromic acid beingparticularly suitable. Tank 16 serves as a reservoir for the solutionwhich is delivered to the sprays by pump 17. Since it is preferable touse a hot (l150 F.) solution the tank 16 is provided with heating means18 which may be a thermostatically controlled steam heating coil. Excesssolution is removed and strip dried prior to entry into stand 128 by hotair drier 19. A conventional chevron type drier is convenient for thispurpose. Excess solution driven from the strip by the air blasts of thedrier may be collected and returned to the tank 16 by suitable bafilesand conduits, not shown.

The chromate solution applied as described serves the double function oftreating the tinned surface and dissipating heat generated in the milland strip by rolling. Successful treatment requires merely that the topand bottom surfaces of the strip be thoroughly wetted. As previouslymentioned, the presence of the oil film does not interfere with actionof the solution. nor is the film disturbed by action of the sprays.While the treating sprays have been shown positioned behind st and 12Aand this practice is preferred, successful result have also beenachieved with sprays located ahead of stand 12A.

The economy of rcducedlast" practices is favored by heavy reductions inthe cold reduction step. However, the amount of reduction made in themill 11 is determined largely by the mechanical properties desired inthe finished product. While reductions as high a about 90% can be made,the formability of plate reduced more than 70% is limited. Presently,the most practical operating range is between 30 and 60% with an optimumbalance of mechanical properties and economy of operation being achievedat about 50%. The thickness of strip introduced into the process isdetermined by the ordered gage of the finished product and the amount ofreduction to be made in the final rolling step; the latter incombination with the ordered weight of coating determines the amount oftin to be deposited in the coating step.

The preferred practices of our invention are summarized in the followingspecific example:

Tin plate ordered to lb. basis Weight and 0.25 lb./bb. coating weightand intended for carbonated beverage can bodies is produced byprocessing a suitable low carbon, low metalloid steel strip through thesequence of operations described above. Since the intended use of thisplate requires an optimum balance of strength and formability, thereduction to be taken at mill 11 is set at Accordingly, the trip isinitially rolled to 90 lb. basis weight, about 0.010 inch thick, and iselectroplated with tin to a nominal coating weight of 0.5 lb./bb.Following plating, and heat-brightening, if the latter step is included,the coated strip is pre-oiled by passing through an electrostatic oileroperated to apply a film of cottonseed oil of between 1.2 and 1.4gms./bb. Alternatively, this quantity of oil can be applied by treatingthe strip with a suitable emulsion of cottonseed oil and water. Theoiled strip is then cold reduced 50% in a suitable two-stand tandemmil]; about 99.5% of the reduction being taken on the first stand, theremainder on the second stand. The strip is maintained under tension andin a substantially horizontal passline during this operation inaccordance with known cold rolling practices.

In the rolling of tin coated strip, it is preferable to use smooth workrolls in the first stand and slightly roughened rolls in the second. Asthe strip emerges from the first stand of the mill, it is thoroughlywetted with a hot (140 F.) aqueous solution containing 1.75% by weightchromic acid applied to its top and bottom surfaces by sprays at a rateof about 10 gallons per hour. Excess solution is removed and the stripdried before entering the second stand of the mill. The rolling reducesthe strip to a finish gage of 45 lb. basis weight (about 0.005 inch) anda finish coating weight of 0.25 lb./bb. Tests have shown the resultingproduct carries a film of about 0.7 gm./1bb. of cottonseed oil and anunderlying film containing from 0.5 to 0.6 mg. per sq. ft. of chromiumexisting probably as a complex oxide with tin. The latter is sufiicientto maintain the surface substantially free of discoloration duringstorage and even when baked in air for 20 minutes at 420 F. Thelubricity, lacquerability, and solderability of the product are theequivalent of conventional tin plate, while the power requirements inthe rolling operation are less than when the steel strip is reduced tofinish-gage prior to tinning. Substantially the same results areobtained when palm oil is substituted for cottonseed oil in thepre-oiling step.

The practices of the invention of course are not limited to the grade ofplate of the example. Other grades, for example or lb. plate carrying0.5 or 1.0 lb. of tin per bb., can be produced by adjusting the gage ofthe entering steel stock and the amount of tin applied in the platingstep. The mechanical properties of the steel base can be varied byadjusting the amount of cold reduction; the amount of oil carried on thefinished product can be varied by adjusting the film applied in thepre-oiling step as previously explained.

While we have shown and described certain specific embodiments of ourinvention, it is obvious that modifications can be made withoutdeparting from the scope of the appended claims.

We claim:

1. In the method for producing a base box of tin plate characterized byrolling a steel strip to an intermediate gage, coating the steel withtin, and cold reducing the tin coated steel to final gage and coatingweight, the improvement comprising applying to the tin coated stripprior to the cold reduction thereof a film of oil in amounts between 1.0and 5.0 gms. per base box, and treating the oiled surface during saidcold reduction with an aqueous chromate containing solution.

2. The method of claim 1 in which the oil applied in the pre-oiling stepis selected from the group consisting of palm oil and cottonseed oil.

3. The method of claim 1 in which the treating solution consists of anaqueous solution containing 1 to 2 percent by weight chromic acid.

4. The method of claim 1 in which the tinned and preoiled strip is coldreduced between about 30 and 70 percent.

5. In the method for producing a base box of tin plate characterized byrolling a steel strip to an intermediate gage, coating the steel withtin and cold reducing the tin coated strip to finish gage and coatingweight in two stages, the improvement comprising applying between 1.0and 5.0 gms. per base box of an oil selected from the group consistingof palm oil and cottonseed oil to the tinned strip prior to coldreduction thereof and treating the tinned and pre-oiled strip with anaqueous chromate containing solution after completion of the first stageof said cold reduction.

6. The method of claim 5 in which the treating solution consists of anaqueous solution containing 1 to 2% by weight chromic acid.

7. The method of claim 5 in which the tinned and pre-oiled strip is coldreduced between a total amount of about 30 and 70% with approximately99% of said total reduction being effected in the first stage of saidtwo stage reduction.

(References on following page) 5 6 References Cited 3,110,413 11/1963McKay et a1. 29-528 DaVlS 2,850,999 9/1958 Kaplan et a1 29528 CHARLES W.LANHAM, Primary Examiner.

3,050,847 8/1962 Hill 29-5 5 E. M. COMBS, Assistant Examiner.

1. IN THE METHOD FOR PRODUCING A BASE BOX OF TIN PLATE CHARACTERIZED BYROLLING A STEEL STRIP TO AN INTERMEDIATE GAGE, COATING THE STEEL WITHTIN, AND COLD REDUCING THE TIN COATED STEEL TO FINAL GAGE AND COATINGWEIGHT, THE IMPROVEMENT COMPRISING APPLYING TO THE TIN COATED STRIPPRIOR TO THE COLD REDUCTION THEREOF A FILM OF OIL IN AMOUNTS BETWEEN 1.0AND 5.0 GMS. PER BASE BOX, AND TREATING THE OILED SURFACE DURING SAIDCOLD REDUCTION WITH AN AQUEOUS CHROMATE CONTAINING SOLUTION.